Carbon nanotube field emitter and preparation method thereof

ABSTRACT

A method for making a carbon nanotube field emitter is provided. A carbon nanotube film is dealed with a carbon nanotube film in a circumstance with a temperature ranged from 1400 to 1800° C. and a pressure ranged from 40 to 60 MPa to form at least one first carbon nanotube structure. The at least one first carbon nanotube structure is heated to graphitize the at least one first carbon nanotube structure to form at least one second carbon nanotube structure. At least two electrodes is welded to fix one end of the at least one second carbon nanotube structure between adjacent two electrodes to form a field emission preparation body. The field emission preparation body has a emission end. The emission end is bonded to form a carbon nanotube field emitter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. § 119 fromChina Patent Application No. 201910642083.7 filed on Jul. 16, 2019, inthe China National Intellectual Property Administration, the contents ofwhich are hereby incorporated by reference. This application is relatedto commonly-assigned applications entitled, “CARBON NANOTUBE FIELDEMITTER AND PREPARATION METHOD THEREOF”, filed Feb. 18, 2005 Ser. No.11/061,677; “CARBON NANOTUBE FIELD EMITTER AND PREPARATION METHODTHEREOF”, filed Feb. 18, 2005 Ser. No. 11/061,434.

FIELD

The present disclosure relates to an evaporating source for a carbonnanotube field emitter and preparation method thereof.

BACKGROUND

In recent years, due to the research and development in carbon nanotubesand nanomaterials, the broad application prospects of the novelmaterials are constantly emerging. For example, due to the uniqueelectromagnetic, optical, mechanical, and chemical properties of thecarbon nanotubes, a large number of applications have been developed infield emission electron sources, sensors, new optical materials, andsoft ferromagnetic materials.

The field emission characteristics of the carbon nanotube have broadapplication prospects in fields such as field emission planar displaydevices, electric vacuum devices, and high-power microwave devices.Conventionally, a carbon nanotube film is used as a field emitter. Sincethe carbon nanotube film has a low density and the carbon nanotubes inthe carbon nanotube film have growth defects, the finishing product of acarbon nanotube field emitter may has poor stability and short life. Inaddition, the carbon nanotube film is adhered to a surface of theelectrode by an adhesive. Thus, the carbon nanotubes can be easilyextracted during field emission, and the carbon nanotube field emitterhas poor stability and short life.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof embodiment, with reference to the attached figures.

FIG. 1 is a flowchart of one embodiment of a method for making a carbonnanotube field emitter.

FIG. 2 is an SEM image of a carbon nanotube drawn film.

FIG. 3 is a side view of carbon nanotube segment.

FIG. 4 is a side view of one embodiment of a field emission preparationbody.

FIG. 5 is a side of one embodiment of the carbon nanotube field emitter.

FIG. 6 is an SEM image of one embodiment of the carbon nanotube fieldemitter.

FIG. 7 is an SEM image of one embodiment of the carbon nanotube fieldemitter.

FIG. 8 is an SEM image of a field emission end of the carbon nanotubefield emitter.

FIG. 9A is an SEM image of a emission end of the field emissionpreparation body after cutting by a laser.

FIG. 9B is a partial enlargement SEM image FIG. 9A.

FIG. 10A is an SEM image of a emission end of the field emissionpreparation body after ultrasonically cleaning.

FIG. 10B is a partial enlargement SEM image FIG. 10A.

FIG. 11 is a electron emission current change curve graph of a carbonnanotube field emitter with time.

FIG. 12 is a current change curve graph of the carbon nanotube fieldemitter in a vacuum with voltage.

FIG. 13 is a current change curve graph of the carbon nanotube fieldemitter in a vacuum with time.

FIG. 14 is a graph showing changes in applied voltage and working timeof a carbon nanotube field emitter.

FIG. 15 is a graph showing changes in voltage and working time of carbonnanotube field emitters under different degrees of vacuum environment.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean “at least one”.

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale, and the proportions of certain parts maybe exaggerated to illustrate details and features of the presentdisclosure better.

Several definitions that apply throughout this disclosure will now bepresented.

The term “comprise” or “comprising” when utilized, means “include orincluding, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in the so-described combination,group, series, and the like.

In FIG. 1, one embodiment is described in relation to a method formaking a carbon nanotube field emitter. The method comprises steps of:

step (S1), handling a carbon nanotube film in an environment of atemperature ranged from 1400 to 1800° C. and a pressure ranged from 40to 60 MPa to form at least one first carbon nanotube structure;

step (S2), heating the at least one first carbon nanotube structure tographitize the first carbon nanotube structure thereby forming form atleast one second carbon nanotube structure;

step (S3), welding at least two electrodes to fix one end of the atleast one second carbon nanotube structure between the at least twoelectrodes to form a field emission preparation body, wherein the fieldemission preparation body comprises a emission end; and

step (S4), bonding the emission end of the field emission preparation toform a carbon nanotube field emitter.

In step (S1), the carbon nanotube film comprises a plurality of carbonnanotube drawn film, and the plurality of carbon nanotube drawn filmstacked with each other. A thickness of the carbon nanotube filmlaminated is ranged from about 1 mm to about 10 mm. The carbon nanotubefilm is extruded by a roll under a pressure of 40-60 MPa at atemperature of 1400-1800° C. for 5-10 min to increase a density of thecarbon nanotube film and form the first carbon nanotube structure. Thedensity of the first carbon nanotube structure is greater than or equalto 1.6 g/m³. The first carbon nanotube structure has a thickness rangedform about 10 micrometers to about 1 millimeter. In one embodiment, thecarbon nanotube film is treated for 6 min under a temperature of 1600°C. and a pressure of 50 MPa to form the first carbon nanotube structure,a thickness of the first carbon nanotube structure is about 50 μm, andthe density of the first carbon nanotube structure was 1.6 g/m³.

The carbon nanotube drawn film can be formed by the substeps of: (a)selecting one or more carbon nanotubes having a predetermined width fromthe super-aligned array of carbon nanotubes; and (b) pulling the carbonnanotubes to form carbon nanotube segments that are joined end to end atan uniform speed to achieve a uniform carbon nanotube drawn film.

In step (a), the carbon nanotube segments having a predetermined widthcan be selected by using a tool such as an adhesive tape, a tweezers, ora clamp to contact the super-aligned array.

In step (b), the pulling direction is substantially perpendicular to thegrowing direction of the super-aligned array of carbon nanotubes. Eachcarbon nanotube segment includes a plurality of carbon nanotubesparallel to each other.

More specifically, during the pulling process, as the initial carbonnanotube segments are drawn out, other carbon nanotube segments are alsodrawn out end to end due to van der Waals attractive force between endsof adjacent segments. This process of drawing ensures a substantiallycontinuous and uniform carbon nanotube film having a predetermined widthcan be formed. The carbon nanotube drawn film comprises a plurality ofcarbon nanotubes joined ends to ends. The carbon nanotubes in the carbonnanotube film are all substantially parallel to the pulling/drawingdirection of the carbon nanotube drawn film, and the carbon nanotubedrawn film produced in such manner can be selectively formed to have apredetermined width. The carbon nanotube drawn film formed by thepulling/drawing method has superior uniformity of thickness andconductivity over a typical disordered carbon nanotube drawn film.Further, the pulling/drawing method is simple, fast, and suitable forindustrial applications.

The width of the carbon nanotube drawn film depends on a size of thecarbon nanotube array. The length of the carbon nanotube film can bearbitrarily set, as desired. In one embodiment, when the substrate is a4-inch P-type silicon wafer as in the present embodiment, the width ofthe carbon nanotube drawn film is in an approximate range from 0.5nanometers to 10 centimeters, and the thickness of the carbon nanotubedrawn film is in an approximate range from 0.5 nanometers to 10 microns.

Referring to FIG. 2 and FIG. 3, each carbon nanotube drawn filmcomprises a plurality of successive and oriented carbon nanotubes joinedend to end by van der Waals attractive force. Each carbon nanotube drawnfilm comprises a plurality of successively oriented carbon nanotubesegments 143 joined end-to-end by van der Waals attractive forcetherebetween. Each carbon nanotube segment 143 includes a plurality ofcarbon nanotubes 145 parallel to each other, and combined by van derWaals attractive force therebetween. The carbon nanotube segments 143can vary in width, thickness, uniformity and shape. The carbon nanotubes145 in the carbon nanotube drawn film 143 are also oriented along apreferred orientation.

The carbon nanotube drawn film comprises a plurality of carbon nanotubesthat can be arranged substantially parallel to a surface of the carbonnanotube drawn film. A large number of the carbon nanotubes in thecarbon nanotube drawn film can be oriented along a preferredorientation, meaning that a large number of the carbon nanotubes in thecarbon nanotube drawn film are arranged substantially along the samedirection. An end of one carbon nanotube is joined to another end of anadjacent carbon nanotube arranged substantially along the same directionby Van der Waals attractive force. A small number of the carbonnanotubes are randomly arranged in the carbon nanotube drawn film, andhas a small if not negligible effect on the larger number of the carbonnanotubes in the carbon nanotube drawn film arranged substantially alongthe same direction.

The carbon nanotube drawn film is capable of forming a free-standingstructure. The term “free-standing structure” can be defined as astructure that does not have to be supported by a substrate. Forexample, a free standing structure can sustain the weight of itself whenit is hoisted by a portion thereof without any significant damage to itsstructural integrity. So, if the carbon nanotube drawn film is placedbetween two separate supporters, a portion of the carbon nanotube drawnfilm, not in contact with the two supporters, would be suspended betweenthe two supporters and yet maintain film structural integrity. Thefree-standing structure of the carbon nanotube drawn film is realized bythe successive carbon nanotubes joined end to end by Van der Waalsattractive force.

Some variation can occur in the orientation of the carbon nanotubes inthe carbon nanotube drawn film. Microscopically, the carbon nanotubesoriented substantially along the same direction may not be perfectlyaligned in a straight line, and some curve portions may exist. It can beunderstood that some carbon nanotubes located substantially side by sideand oriented along the same direction in contact with each other cannotbe excluded.

The carbon nanotube film comprises at least two stacked carbon nanotubedrawn films. Adjacent drawn carbon nanotube films can be combined byonly Van der Waals attractive forces therebetween without the need of anadditional adhesive. An angle between the aligned directions of thecarbon nanotubes in the two adjacent carbon nanotube drawn films canrange from about 0 degrees to about 30 degrees. In one embodiment, theangle between the aligned directions of the carbon nanotubes in the twoadjacent carbon nanotube drawn films is 0 degrees.

Further, the method comprises a step of: depositing a carbon layer on asurface of the first carbon nanotube structure after step S1. The carbonlayer is uniformly coated on the surface of the first carbon nanotubestructure. The carbon layer can further increase the mechanicalproperties of the first carbon nanotube structure, thereby increasingthe emission stability of the carbon nanotube field emitter.

In step (S2), the first carbon nanotube structure is heated tographitize the first carbon nanotube structure by the followingsubsteps: (S21) placing the first carbon nanotube structure in agraphite crucible and then placing the graphite crucible in agraphitization furnace; (S22) heating the first carbon nanotubestructure to a temperature ranging from about 2000° C. to about 3000° C.for about 10 to 300 minutes in the graphite furnace with an inert gas;(S23) cooling to room temperature to form the second carbon nanotubestructure. Then, the second carbon nanotube structure can be took out ofthe graphite furnace. In one embodiment, the first carbon nanotubestructure is placed in the graphite crucible and then placed thegraphite crucible in the graphitization furnace, then the first carbonnanotube structure is heated to about 2800° C. for about 60 minutesunder argon gas protection, and the temperature of the graphitizationfurnace is cooled to room temperature to form the second carbon nanotubestructure. The second carbon nanotube structure is then taken out of thegraphitization furnace.

The heat treatment of the first carbon nanotube structure can removehigh temperature volatile impurities (such as metal catalysts) in thefirst carbon nanotube structure to graphitize the first carbon nanotubestructure, and eliminate microscopic structural defects.

In step (S3), welding at least two electrodes to fix one end of at leastone second carbon nanotube structure between adjacent two electrodes toform a field emission preparation body by spot welding or laser welding.The field emission preparation body has a emission end.

Referring to FIG. 4, the second carbon nanostructure comprises a firstend 12 and a second end 14, and the first end 12 is opposite to thesecond end 14. The at least two electrodes 22 are fixed together by spotwelding or laser welding, thereby fixing at least one first end 12between the adjacent two electrodes 22 and exposing the second end 14 asthe emission end of the field emission preparation body.

The first end 12 of the second carbon nanostructure is fixed between theadjacent two electrodes 22 by spot welding comprises the followingsubsteps: S311, placing the first end 12 of the at least one secondcarbon nanostructure between the adjacent two electrodes 22, wherein theadjacent two electrodes 22 clamps the first end 12, and the second end14 is exposed to form an emission unit; S312, placing the emission unitbetween a fixed welding head and a movable spot welding head, anddriving a pressure driving device to press the movable spot welding headagainst the fixed spot welding head; S313, controlling a spot welderoutput a voltage and a current to weld the adjacent two electrodes 22together to fix the first end 12 of the at least one the second carbonnanostructure.

In step S311, when the first end 12 of the second carbon nanotubestructure is placed between the adjacent two electrodes 22, theplurality of carbon nanotubes of the second carbon nanotube structureextend along a length direction of the second end 14. That is, theextending direction of the carbon nanotubes in the second carbonnanostructure is parallel to the electron emission direction of thecarbon nanotube field emitter. In one embodiment, each first end 12 isplaced between two electrodes 22.

In step S312, when the pressure driving device is driven, a pressurebetween the movable spot welding head and the fixed spot welding head isranged from about 50N to about 20N. In step S313, welding the loweredges of the two electrodes 22 to weld the two electrodes 22 together tofix the first end 12 of the second carbon nanotube structure. The outputvoltage is ranged from about 2.3V to about 10V, the output current is800 A, and the output voltage and current release time are controlled ata range about 200 ms to 300 ms.

Furthermore, when the carbon nanotube field emitter comprises aplurality of the emission units, the method of making for the carbonnanotube field emitter may comprises a step of repeatedly stacking aplurality of the emission units after step S311.

When the first end 12 of the at least one second carbon nanotubestructure is fixed between the at least two electrodes 22 by laserwelding comprises the following substeps: S321, placing the first end 12of the at least one second carbon nanotube structure between theadjacent two electrodes 22, wherein the adjacent two electrodes 22clamps the first end 12, and the second end 14 is exposed to form anemission unit; S322, clamping and fixing the emitting unit with a clamp;S323, welding the adjacent two electrodes 22 by laser irradiation to fixthe first end 12 of the at least one second carbon nanotube structure.

In step S321, when the first end 12 of the second carbon nanotubestructure is placed between the two electrodes 22, the plurality ofcarbon nanotubes of the second carbon nanotube structure extend along alength direction of the second end 14. That is, the extending directionof the carbon nanotubes in the second carbon nanostructure is parallelto the electron emission direction of the carbon nanotube field emitter.In one embodiment, each first end 12 is placed between two electrodes22.

In step S323, the laser may be any type of laser as long as heating canbe produced, such as, a carbon dioxide laser, a semiconductor laser, anultraviolet laser, or a yttrium aluminum garnet (YAG) laser. A diameterof the laser beam ranges from about 10 micrometers to about 400micrometers. A power of the laser beam ranges from about 3.6 watts toabout 1.5 kilowatts. A laser pulse frequency of the laser beam rangesfrom about 20 kHz to 40 kHz. In one embodiment, the laser is the YAGlaser, a wavelength of the YAG laser is 1.06 μm, a laser beam spotdiameter of the YAG laser is 20 μm, a power of the YAG laser is 1.5 KW,and a laser pulse frequency of the YAG laser is 20 kHz.

Furthermore, when the carbon nanotube field emitter comprises aplurality of the emission units, the method of making for the carbonnanotube field emitter may comprises a step of repeatedly stacking aplurality of the emission units after step S321.

The material of the electrode 22 may be gold, silver, copper, or nickel.A thickness of the electrode 22 ranges from about 50 micrometers toabout 150 micrometers. The electrode 22 can be a sheet-like structure ora flattened tubular structure. When the electrode 22 is a flattenedtubular structure, the first end 12 of the at least one second carbonnanotube structure is disposed in the intermediate space of theflattened tubular structure and clamped by the flattened tubularstructure. The first end 12 of the at least one second carbon nanotubestructure is fixed in the flattened tubular structure by welding thebottom of the flattened tubular structure. In one embodiment, theelectrode 22 consists of a flattened nickel tube. The first end 12 ofthe at least one second carbon nanotube structure is disposed in theintermediate space of the flattened nickel tube and is clamped by theflattened nickel tube, and then the first end 12 of the at least onesecond carbon nanotube structure is fixed in the flattened nickel tubeby welding the flattened nickel tube. A wall thickness of the nickeltube is 100 microns.

Further, before step S2, the method comprises a step of: cutting thesecond carbon nanotube structure. In this step, the second carbonnanotube structure is cut to a desired size as needed. In oneembodiment, the second carbon nanotube structure is cut into a sheetstructure. The length of the sheet structure is about 4 mm, and thewidth of the sheet structure is about 2 mm.

In step S4, the emission end of the field emission preparation body,that is, the second end 14 of the second carbon nanotube structure, maybe treated by a tape or a liquid glue. A part of carbon nanotube of thesecond end 14 are pulled upright and form a plurality of burrs bypeeling off the tape or the liquid. In one embodiment, the tape isdirectly adhered to the surface of the second end 14, and then the tapeis peeled off to surface the second end 14. A part of the carbonnanotubes are pulled upright.

The carbon nanotube field emitter formed by using the liquid gluecomprises following substeps: S41, a liquid glue is disposed on thesurface of the second end 14; S42, curing the liquid glue; S43, peelingoff the cured liquid glue on the surface of the second end 14 to pullupright the carbon nanotubes on the surface of the second end 14. Theliquid glue may be a thermosetting glue, a thermoplastic glue or anultraviolet curing glue. Specifically, the liquid glue may be liquidsilica glue, polysiloxane ester liquid crystal (PMMS), ultravioletcurable glue or the like. In step S42, the thermosetting glue is curedby a stepwise heating. The thermoplastic glue is cured by cooling. Theultraviolet curing glue can be cured by ultraviolet light irradiation.Since a portion of the liquid glue penetrates into gaps of the secondend 14, the bonding force between the cured liquid glue and the second14 is strong. In step S43, the cured liquid glue may be directly peeledoff the cured liquid glue with tweezers or other tools. A part of thecarbon nanotubes on the surface of the second end 14 is pulled uprightby peeling off the cured liquid glue.

Further, after step S3 before step S4, the method comprises a step of:cutting the second end 14 of the field emission preparation body with alaser.

The second end 14 is cut along a predetermined cutting line by a laserbeam from a laser controller controlled by a computer. The laser may beany type of laser as long as the heating can be produced, such as, acarbon dioxide laser, a semiconductor laser, an ultraviolet laser, or ayttrium aluminum garnet (YAG) laser. The wavelength, power, scanningspeed, and laser beam spot diameter of the laser beam can be setaccording to actual needs. The cutting line is a curve. The curve is acombination of a plurality of zigzags, a plurality of elliptical shapes,a plurality of semicircles, or any other pattern. In one embodiment, thecutting line comprises a plurality of zigzags. A distance from a tip ofthe cutting line to the top of the electrode 22 is ranged from about 100micrometers to about 5 millimeters. In one embodiment, the distance fromthe tip of the cutting line to the top of the electrode 22 is rangedfrom about from 100 micrometers to about 1 millimeter. In anotherembodiment, the distance from the tip of the cutting line to the top ofthe electrode 22 is 250 micrometers.

Further, after the second end 14 is cut by laser, the method comprises astep of: ultrasonically cleaning the second end 14. Ultrasonicallycleaning the second end 14 can remove loose carbon nanotubes andimpurities in the second end 14 which is beneficial to improve the fieldemission performance and lifetime of the carbon nanotube field emitter.

In one embodiment, the field emission preparation body cut by laser isplaced in an organic solvent for ultrasonic cleaning for about 15minutes to about 1 hour, and then the field emission preparation body isdried. The ultrasonic cleaning frequency is ranged from about 3 kHz to10 kHz, and the organic solvent is deionized water.

Further, the method comprises a step of: depositing a carbon layer on asurface of the at least one graphitized carbon nanotube wire after stepS2. The carbon layer is uniformly coated on the surface of the at leastone graphitized carbon nanotube wire to form a carbon nanotube wirecomposite structure. The carbon layer can further increase themechanical properties of the graphitized carbon nanotube wire, therebyincreasing the emission stability of the carbon nanotube field emitter.

Referring to FIG. 5-6, the carbon nanotube field emitter 100 prepared bythe method for making the carbon nanotube field emitter is provided. Thecarbon nanotube field emitter comprises at least two electrodes 22 andat least one carbon nanotube structure. The carbon nanotube structurecomprises a first end 12 and a field emission end 16, the first end 12is opposite to the field emission end 16. The first end 12 of the atleast one carbon nanotube structure is fixed between two adjacentelectrodes 22, and the field emission end 16 of the at least one carbonnanotube structure is exposed from the at least two electrodes 22 toemit electrons. A density of the carbon nanotube structure is largerthan or equal to 1.6 g/m³ or more.

Referring to FIG. 7˜8, the field emission end 16 comprises a pluralityof protrusions and a plurality of burrs. The plurality of protrusionsmay be in a zigzag shape, a semicircular shape or other irregular shapeor the like. The plurality of burrs are disposed on the surface of thefield emission end 16. Each burr is a single carbon nanotube or a bundleof carbon nanotubes formed from a plurality of carbon nanotubes. Theplurality of burrs of the field emission end 16 can reduce a surfacearea of the field emission tip, thereby making the local electric fieldmore concentrated and increasing the field emission efficiency.

The carbon nanotube structure comprises a plurality of carbon nanotubedrawn films, and the plurality of carbon nanotube films are stacked witheach other. The number of layers of the carbon nanotube drawn film inthe carbon nanotube structure is 2-10. The density of the carbonnanotube structure is larger than and equal to 1.6 g/m³. In oneembodiment, a thickness of the carbon nanotube structure is 50 μm. Thedensity of the carbon nanotube structure is 1.6 g/m³.

Referring to FIG. 2, the carbon nanotube drawn film comprises aplurality of carbon nanotubes that can be arranged substantiallyparallel to a surface of the carbon nanotube drawn film. A large numberof the carbon nanotubes in the carbon nanotube drawn film can beoriented along a preferred orientation, meaning that a large number ofthe carbon nanotubes in the carbon nanotube drawn film are arrangedsubstantially along the same direction. An end of one carbon nanotube isjoined to another end of an adjacent carbon nanotube arrangedsubstantially along the same direction by Van der Waals attractiveforce. A small number of the carbon nanotubes are randomly arranged inthe carbon nanotube drawn film, and has a small if not negligible effecton the larger number of the carbon nanotubes in the carbon nanotubedrawn film arranged substantially along the same direction.

The carbon nanotube drawn film is capable of forming a free-standingstructure. The term “free-standing structure” can be defined as astructure that does not have to be supported by a substrate. Forexample, a free standing structure can sustain the weight of itself whenit is hoisted by a portion thereof without any significant damage to itsstructural integrity. So, if the carbon nanotube drawn film is placedbetween two separate supporters, a portion of the carbon nanotube drawnfilm, not in contact with the two supporters, would be suspended betweenthe two supporters and yet maintain film structural integrity. Thefree-standing structure of the carbon nanotube drawn film is realized bythe successive carbon nanotubes joined end to end by Van der Waalsattractive force.

Some variation can occur in the orientation of the carbon nanotubes inthe carbon nanotube drawn film. Microscopically, the carbon nanotubesoriented substantially along the same direction may not be perfectlyaligned in a straight line, and some curve portions may exist. It can beunderstood that some carbon nanotubes located substantially side by sideand oriented along the same direction in contact with each other cannotbe excluded.

The carbon nanotube film comprises at least two stacked carbon nanotubedrawn films. Adjacent drawn carbon nanotube films can be combined byonly Van der Waals attractive forces therebetween without the need of anadditional adhesive. An angle between the aligned directions of thecarbon nanotubes in the two adjacent carbon nanotube drawn films canrange from about 0 degrees to about 30 degrees. In one embodiment, theangle between the aligned directions of the carbon nanotubes in the twoadjacent carbon nanotube drawn films is 0 degrees. A plurality of carbonnanotubes in the carbon nanotube structure extend along the lengthdirection of the field emission end 16. That is, the extending directionof the carbon nanotubes in the carbon nanotube structure is parallel tothe electron emission direction of the carbon nanotube field emitter.

The electrode 22 can be a sheet structure or a flattened tubularstructure. The material of the electrode 22 may be gold, silver, copper,or nickel. A thickness of the electrode 22 ranges from about 50micrometers to about 150 micrometers. When the electrode 22 is aflattened tubular structure, the first end 12 is disposed in theintermediate space of the flattened tubular structure and is clamped bythe flattened tubular structure, and then the first end 12 is fixed inthe flattened tubular structure by welding the bottom of the flattenedtubular structure. In one embodiment, the electrode 22 consists of aflattened nickel tube. The first end 12 is disposed in the intermediatespace of the flattened nickel tube and is clamped by the flattenednickel tube, and then the first end 12 is fixed in the flattened nickeltube by welding the bottom of the flattened nickel tube. A wallthickness of the nickel tube is 100 microns.

In one embodiment, the carbon nanotube field emitter comprises a carbonlayer. The carbon layer is uniformly coated on at least one surface ofthe carbon nanotube structure. The carbon layer can further increase themechanical properties of the carbon nanotube structure, therebyincreasing the emission stability of the carbon nanotube field emitter.

Embodiment 1

The carbon nanotube film is heated at a temperature of 1600° C. and apressure of 50 MPa for 6 min to form a first carbon nanotube structure.The carbon nanotube film are formed by stacking three carbon nanotubedrawn films. The first carbon nanotube structure is placed in thegraphite crucible and then the graphite crucible is in thegraphitization furnace, then the first carbon nanotube structure isheated to about 2800° C. for about 60 minutes under argon gasprotection, and the temperature of the graphitization furnace is cooledto room temperature to form the second carbon nanotube structure. Thesecond carbon nanotube structure is then taken out of the graphitizationfurnace. A thickness of the second carbon nanotube structure is about 50microns. The second carbon nanotube structure is cut into a sheetstructure. The length of the sheet structure is about 4 mm, and thewidth of the sheet structure is about 2 mm. A pure nickel tube isflattened to sandwich the first end of the second carbon nanostructureto form an emission unit. A thickness of the pure nickel tube is about100 microns. Three emission units are stacked, and the three emissionunits are sandwiched by a clamp. Then, the lower edges of stacked threeemission units is irradiated by the YAG laser beam. The flattened nickeltubes are welded together and a plurality of second ends are fixedbetween two adjacent electrodes to form a field emission preparationbody. The field emission preparation comprises a emission end, that is,the second end of the first carbon nanotube structure. A wavelength ofthe YAG laser is 1.06 μm, a laser beam spot diameter of the YAG laser is30 μm, a power of the YAG laser is 12 W, and a laser pulse frequency ofthe YAG laser is 20 kHz. Then, the second end 14 is cut by the YAG laserto form a plurality of zigzags. the field emission preparation body cutby laser is placed in an organic solvent for ultrasonic cleaning forabout 15 minutes to about 1 hour, and then the field emissionpreparation body is dried. A tape is directly adhered to the surface ofthe second end 14. A part of the carbon nanotubes are pulled upright toform a carbon nanotube field emitter by peeling off the tape from thesurface the second end 14.

FIG. 9A and FIG. 9B are scanning electron micrographs of the emittingend of the field emission preparation body after laser beam cutting.FIG. 10A and FIG. 10B are scanning electron micrographs of the emittingend of the field emission preparation body after ultrasonic cleaning. Asshown in FIG. 9A and FIG. 9B, the emission end of the field emissionpreparation after laser beam cutting has a small amount of impurities.Comparing FIG. 9A and FIG. 9B with FIG. 10A and FIG. 10B, it can be seenthat after the ultrasonic cleaning, the impurities at the emitting endof the field emission preparation body are removed.

FIG. 11 is a electron emission current change curve graph of a carbonnanotube field emitter with time. As shown in FIG. 11, the fieldemission current of the carbon nanotube field emitter is 2.5 mA to 3.5mA in the test time of 20,000 seconds. It can be seen that theefficiency of electron emission of the carbon nanotube field emitter ishigh, and the emission characteristics change little with time, and thecarbon nanotube field emitter has stable field emission.

FIG. 12 is a current change curve graph of the carbon nanotube fieldemitter in a vacuum with voltage. As shown in FIG. 12, a current curveof the carbon nanotube field emitter after 100 hours is basically thesame as an original current curve. FIG. 13 is a current change curvegraph of the carbon nanotube field emitter in a vacuum with time. It canbe seen that the electron emission current does not change much withtime. FIG. 12 and FIG. 13 illustrate that the carbon nanotube fieldemitter has a higher efficiency of emitting electrons in a vacuum, andthe emission characteristics do not change much with time.

Referring to FIG. 14, it can be seen from the figure that the voltageapplied to the carbon nanotube field emitter does not change much withtime, indicating that the emission stability of the carbon nanotubefield emitter is relatively good.

Referring to FIG. 15, when the degree of vacuum is 1.6×10⁻⁶ Pa, and theemission current is 3 mA, the voltage of the carbon nanotube fieldemitter does not change much with time, indicating that the emissionstability of the carbon nanotube field emitter is good in a vacuum of1.6×10⁻⁶ Pa.

The carbon nanotube field emitter provided by the invention has thefollowing advantages: Firstly, the density of the carbon nanotubestructure in the carbon nanotube field emitter is large. Thus, theelectron emission current can be increased, and the volume of the carbonnanotube field emitter can be reduced. Secondly, the heating treatmentof carbon nanotube film can remove the catalyst and repair the defectsof the carbon nanotubes. Therefore, the stability and service life ofthe carbon nanotube field emitter can be improved. Thirdly, the carbonnanotube v can be firmly fixed between the adjacent two electrodes bythe welding the electrode, and the bonding force between the carbonnanotube structure and the electrode can be improved. Thus, the carbonnanotube structure does not detach from the electrode during electronemission, and the emission efficiency and service life of the carbonnanotube field emitter can be improved.

Even though numerous characteristics and advantages of certain inventiveembodiments have been set out in the foregoing description, togetherwith details of the structures and functions of the embodiments, thedisclosure is illustrative only. Changes may be made in detail,especially in matters of arrangement of parts, within the principles ofthe present disclosure to the full extent indicated by the broad generalmeaning of the terms in which the appended claims are expressed.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may comprise some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. A method for making a carbon nanotube fieldemitter, comprising: S1: handling a carbon nanotube film in anenvironment of a temperature ranged from 1400 to 1800° C. and a pressureranged from 40 to 60 MPa to form at least one first carbon nanotubestructure; S2: heating the at least one first carbon nanotube structureto graphitize the first carbon nanotube structure thereby forming atleast one second carbon nanotube structure; S3: welding at least twoelectrodes to fix one end of the at least one second carbon nanotubestructure between the at least two electrodes to form a field emissionpreparation body, wherein the field emission preparation body comprisesan emission end; and S4: bonding the emission end of the field emissionpreparation to form a carbon nanotube field emitter.
 2. The method ofclaim 1, wherein the at least one second carbon nanotube structurecomprises a first end and a second end, the first end is opposite to thesecond end, and the first end of the at least one second carbon nanotubestructure is fixed between the at least two electrodes by a spot weldingmethod or a laser welding method.
 3. The method of claim 2, wherein thefirst end of the at least one second carbon nanotube structure is fixedbetween the at least two electrodes by the spot welding method, the spotwelding method comprising steps of: S311: placing the first end of theat least one second carbon nanostructure between the at least twoelectrodes, wherein each of the least two electrode clamps the first endof the at least one second carbon nanotube structure, and the second endis exposed to form an emission unit; S312: placing the emission unitbetween a fixed welding head and a movable spot welding head, anddriving a pressure driving device to press the movable spot welding headagainst the fixed spot welding head; and S313: controlling a spot welderto output a voltage and a current to weld the adjacent two electrodestogether to fix the first end of the at least one second carbon nanotubestructure.
 4. The method of claim 1, wherein the first end of the atleast one second carbon nanotube structure is fixed between the at leasttwo electrodes by a laser welding method, the laser welding methodcomprising steps of: S321: placing the first end of the at least onesecond carbon nanotube structure between the two electrodes, wherein theeach of the at least two electrodes clamps the first end of the at leastone second carbon nanotube structure, and the second end is exposed toform an emission unit; S322: clamping and fixing the emitting unit witha clamp; S323: welding the at least two electrodes by laser irradiationto fix the first end of the at least one second carbon nanotubestructure.
 5. The method of claim 1, further comprising a step ofcutting the second end of the at least one second carbon nanotubestructure with a laser after S3.
 6. The method of claim 2, furthercomprising a step of ultrasonically cleaning the second end of the atleast one second carbon nanotube structure.
 7. The method of claim 1,further comprising a step of depositing a carbon layer on a surface ofthe first carbon nanotube structure.